The long-term goal of this project is obtain a more thorough understanding of how HIV Gag proteins are transported through the cell's cytoplasm and where they are directed. It is clear that cellular proteins are required for these processes. One such cellular protein found to interact with retroviral Gag proteins is Ubc9, a nuclear pore-associated E2 Sumo conjugating enzyme. The involvement of Ubc9 and sumoylation of HIV-1 Gag proteins will be investigated as to its relevance in HIV replication. The hypothesis proposed is that Ubc9 promotes the association between HIV Gag proteins and the nuclear compartment. Such an association may be essential for viral RNA packaging during virus assembly. Such a model would explain how Gag proteins are able to compete with ribosomes for viral RNA packaging or for translation. Alternatively Ubc9 may be important for the nuclear targeting of the pre-integration complex during the early stages of the viral life cycle. These ideas are based on the observations that many cellular proteins that sumoylated by Ubc9 are transported to the nuclear compartment. Secondly, over-expression of Ubc9 and Gag proteins results in a dramatic accumulation of Gag proteins either in or juxtaposed to the nuclear compartment. The studies proposed in this application focus on Ubc9-HIV interactions and the relevance of the interaction to HIV replication. We will characterize the interaction between Ubc9 and HIV proteins by identifying the interactions domains, by demonstrating that Ubc9 and HIV Gag co-localize in cells and by determining whether HIV Gag is sumoylated by Ubc9. Secondly, the biological significance of this interaction will be demonstrated by showing that an inability to interact with Ubc9 is lethal to the virus. The results obtained from these studies will provide important information about how Gag proteins function within cells and may provide a framework for developing novel therapeutic strategies to combat HIV replication. [unreadable] [unreadable]